What happens when you use a “bad” combination of ingredients on your skin? One skincare expert weighs in

Dr Vanita Rattan — the cosmetic formulator specialising in skin of colour, YouTuber and The Hyperpigmentation Clinic founder — discusses the dos and don’ts of skincare combinations in this extract from her new book, Skin Revolution.

There are some ingredient combinations you should avoid at all costs and those that will save you time and money. But what actually happens if you layer products that don't play nicely together? 

The best-case scenario is that you will render the ingredients ineffective as they cancel each other out.

In most cases you will see a mild irritation or inflammation, which is a warning sign for you to stop or “titrate” (slowly increase usage) the ingredients.

The worst-case scenario is that inflammatory mediators are released, which trigger the melanocytes and lead to hyperpigmentation in skin of colour.

Dr Vanita Rattan. Photo / Supplied

Here’s a quick guide to the most important ingredients to keep apart on your skin:

COMBINATION 1: Ascorbic acid and niacinamide

(This is the most common combination I get asked about by viewers.)

Old research from the 1960s showed that non-stable vitamin C and niacinamide can irritate the skin, but we use stable forms of both now.

People also say that combining ascorbic acid and niacinamide converts niacinamide to nicotinic acid. However, this only happens at high temperatures over a long period of time. Our skincare is not subjected to these intense conditions.

Having said this, it is important to know there are many forms of vitamin C, all with different optimal pHs. This is why I would not formulate with ascorbic acid and niacinamide in one cream. I would also avoid layering them, because as we do not absorb 100 per cent of a product, some is left on the surface of the skin and you want each active working at their optimal pHs.

I would combine niacinamide with vitamin C derivatives like tetrahexyldecyl (no pH), sodium ascorbyl phosphate (pH 5.5-7), magnesium ascorbyl phosphate (pH 5.5-7) or ascorbic acid (pH 3-3.5). Remember: Niacinamide works best from pH 5-7.

COMBINATION 2: Niacinamide and acids (AHA/BHA)

Low-pH acids do not provide an optimal environment for niacinamide to function. Niacinamide is best combined with neutral pH combinations (pH 5-7).

COMBINATION 3: Retinol and exfoliation (physical/chemical)

The vitamin A family (which includes retinol) increases cell turnover rates, so it helps to bring younger skin to the surface.

This can lead to dryness and sensitivity, though, so you don’t want to further irritate the skin with exfoliation and risk damaging the skin barrier.

COMBINATION 4: Vitamin A and benzoyl peroxide

Benzoyl peroxide actually oxidises retinol and stops it working. It will oxidise all antioxidants including vitamin C, resveratrol and ferulic acid. Benzoyl peroxide is very sensitive and using it at the same time as antioxidants can decrease its effectiveness as an antibacterial.

If you want to use both ingredients for acne, I recommend you apply your benzoyl peroxide, then wait for it to completely dry before applying your antioxidant.

Always top off with a fatty, non-fragrance moisturiser with soothing ingredients, such as panthenol or allantoin, to minimise dryness and irritation.

Benzoyl peroxide also inactivates tretinoin (Retin-A), so don’t use these at the same time. Retinoid-like compounds, however, such as adapalene, are not affected by benzoyl peroxide.

COMBINATION 5: Benzoyl peroxide and exfoliation

Benzoyl peroxide is an antibacterial and clears pores to prevent blocking. I recommend a maximum 2.5 per cent to minimise the chances of irritation. This is great for treating acne but can lead to dry skin and sensitivity.

If the ingredient is too harsh for your skin or the percentage used is too high, you may see flaking. I recommend being gentle with your skin at this point, avoiding exfoliation products, which include glycolic acid and salicylic acid.

COMBINATION 6: Alcohol toners with any active ingredient afterwards

Denatured alcohol is used for its “quick-dry” feel, however, it can end up stripping and dehydrating the skin.

This impairs the skin barrier, delaying skin repair. It can worsen a lot of skin conditions, including making oily skin even oilier.

Although alcohol does allow more absorption of actives, it can damage skin in the process, so you could end up with more issues, including sensitivity

COMBINATION 7: Tranexamic acid and low-pH acids

Tranexamic acid works best at a pH of 7. It is mild on the skin and good for skin of colour. Don’t use it with other low-pH acids (see below), as it will become less effective if it is not at its optimal pH. This is why a cosmetic formulator would not place these tranexamic acids in the same product as the following low-ph acids:

COMBINATION 8: Retinol and acids with low pH

Retinol is drying and can be irritating, which is why I don’t recommend using it with a low-pH acid.

Edited extract from Skin Revolution: The Ultimate Guide to Beautiful and Healthy Skin of Colour by Dr Vanita Rattan, (HarperCollins, $45).

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